1. Field of the Invention
The present invention relates to a vehicle audio system and a reproduction method using same. More particularly, the present invention relates to a rear seat audio system having a deep bass reproduction speaker (“subwoofer”) mounted thereon, which reduces or eliminates inconvenient vibrations created by the subwoofer. The vibrations occur especially when the system supplies a user or passenger in a rear seat with audio information from an audio source such as a CD changer (CDC), a radio tuner, or the like.
Such a rear seat audio system is called a rear entertainment system (RES: Rear Entertainment System), and is generally in a large luxury vehicle.
2. Description of the Related Art
Conventional rear entertainment systems are provided with operating units (including an operating section, a controller, and the like) that are adapted for operations such as selection of an audio source, adjustment of volume and audio quality, or the like, which operations are instructed by a user riding in a rear seat. Also, the systems are provided with a headphone and the like by which the user listens to an audio signal (sound) produced from the selected source. Generally, in known vehicles with such systems, the same kind of apparatus is installed at a front seat area, too. In this case, for the convenience of a driver, a speaker for the front seat area is provided instead of the headphone.
There is a wide variety of arrangements for the speakers. In the typical rear entertainment system, shown in FIG. 2, four speakers 1L, 1R, 2L, and 2R are arranged on the left side and right side of the front seat, and on the left side and right side of the rear seat, respectively. In most cases, there is further provided a deep bass reproduction speaker (subwoofer 3) in the vicinity of the rear seat (in the center thereof).
In the rear entertainment systems as described above, a user in the rear seat or the front seat operates various operating keys disposed in the operating section, and gives the system instructions to select the audio source, or to provide the audio signal supplied from the selected source over the headphone or the speaker. Otherwise, he/she gives instructions for operation (such as seeking up/down, adjustment of the volume or audio quality, or the like) to the audio source, from which audio information is being supplied over the headphone or speaker. Thus, based on these instructions given by the user, the audio source has its operating state set by a controller, and the operating state is recognized or listened to by the user over the headphone or the speaker.
In a case where the user in the rear seat listens to the same audio source (audio signal) as that selected in the front seat, the headphone is not utilized, and the audio signals can be heard from all the speakers. In contrast, when the rear seat user selects an audio source different from that selected by the front seat user, the front seat user listens to the audio source selected on the front side over each speaker, while the rear seat user listens to the audio source selected on the rear side over the headphone. It is noted that if the front seat user changes the source to another while the front and rear seat users are listening to the same source, then audio signals from the new source are supplied through every speaker.
As mentioned above, not only when the rear seat user selects the same source as the front seat user does, but even when he selects the different source from that on the front seat side, the known rear entertainment systems permit the users both in the front and rear seats to listen to the audio information from their selected audio source over the speakers or the headphone.
In the known rear entertainment system as described above having the subwoofer disposed in the vicinity of the rear seat, when the same audio source is selected both by the front and rear seat sides, the users in the front and rear seats can listen to the audio signals from the source over the respective speakers, thus resulting in no problem. However, when the rear seat user selects an audio source different from that selected by the front seat user, the following inconvenience occurs.
That is, when the rear and front seat users select the same audio source (hereinafter referred to as “audio signal A”), the front seat speaker, the rear seat speaker, and the subwoofer each output the audio signal A. In this state, if the rear user selects an audio source (hereinafter referred to as “audio signal B”) different from that on the front side, then the audio signal B is supplied not from the rear seat speaker but from the headphone for the rear seat, whereby the rear seat user can listen to the audio signal B by means of the headphone for the rear seat.
At this time, the subwoofer still provides the audio signal A, which is the same as that supplied on the front side, towards the rear seat. This audio signal from the subwoofer has such deep bass and so much vibration that even when the rear seat user listens to the audio signal B over the headphone, he/she feels the vibrations (the audio signal A) all over his/her body. These vibrations, which differ from the audio signal B in tone, provide the rear seat user with a sense of incongruity upon listening, thereby confusing him/her.
This sense of incongruity occurs not only due to the vibrations caused by the subwoofer, but also due to similar vibrations, for example, caused by a high speed of the vehicle and the like.